J. Eur. Opt. Society-Rapid Publ. 21, 20( 2025) 201
Figure
3. Plot of a typical focus scan depicting the MTF value for a selected spatial frequency m 0 vs. z-axis position relative to the focus point position z( P f) determined using a polynomial fit. intensity / 1
image position / px
Figure 4. Line spread function( LSF) depicting the intensity distribution in the camera image( inset top left).
Figure
5. Waterfall plot of the LSF curves of repeated focus scans displaying the shift of the LSF maximum after changing the ambient temperature. Left: tangential slit object orientation, right: sagittal slit object orientation. Coordinates given refer to the measurement setup coordinate system( cf. Fig. 1).
LSF at the focus point position, the line color denotes the intensity value, and the points marked in red indicate the respective maximum of each LSF plot.
After the temperature change the position of the LSF maximum shifts by 10 px( 1.35 lm) in the horizontal direction perpendicular to the optical axis( y) and 6 px( 0.8 lm) in the vertical direction perpendicular to the optical axis( x). It can be seen that the LSF maximum shift in the vertical direction vanishes after about 10 h whereas the horizontal offset remains. This denotes the different expansion behavior of the components of the experimental setup.
3.2 Focus point shift
Figure 6 shows the results of the 130 repeated focus scans. Like in Figure 5 each line represents a single focus scan and its color the MTF value. The points marked in red indicate the respective MTF maximum of each focus scan plot.